Defence System

ABSTRACT

A defence system  2, 60, 70, 100  comprising a net layer  4, 62, 72  and a buffer layer  6, 64, 74  wherein the buffer layer  6, 64, 74  is provided in front of the net layer  4, 62, 72.

The present invention relates to defence system which may be utilised to protect a vulnerable target, such as a vehicle, building or other object, from damage caused by a shaped-charge warhead, such as a rocket propelled grenade (RPG).

Shaped-charge warheads, such as RPGs are capable of penetrating steel and armour and, therefore, pose a particular problem for tanks and armoured personnel carriers (APC) in combat situations. A shaped-charge warhead consists of a cone-shaped warhead having a quantity of explosive disposed behind a hollow space. The hollow space is typically lined with a compliant material, such as copper. The tip of the cone-shaped warhead is provided with a piezoelectric initiator which generates a firing pulse when a force is applied, i.e. upon impact. When detonated the energy is concentrated to the centre of the charge and it is sufficient to transform the copper into a thin, effectively liquid, shaped-charge jet having a tip speed of up to 121 ms⁻¹. The extremely high pressures generated cause the target material to yield and flow plastically, with devastating effect. To be most effective the shaped-charge has to detonate at the correct distance from the target. If it detonates too close to the target the shaped-charge jet will not have properly formed before hitting the surface and the effect will be lessened. Conversely, if the shaped-charge is detonated too far away from the target surface the shaped-charge jet will have diffused and, again, the effect is lessened.

The fact that shaped-charge warheads must be detonated at a particular distance from the target object has been commonly utilised in defence shields. By providing a preliminary shield at a short distance from the actual armour of the vehicle, or other structure, it is possible to cause the warhead to detonate at a safe distance from the actual armour, with the effect that the charge explodes between the preliminary shield and the armour. In effect, the warhead becomes a conventional grenade, rather than a shaped-charge.

Any preliminary shield which causes premature detonation of the shaped-charge will offer some degree of protection. The shield itself merely needs to cause detonation, it is not meant to act as additional armour. During World War II the German army fitted sheet metal skirts or “Schürzen” on to many of their tanks to act as a preliminary shield. In more recent times it has become common to fit so-called “slat armour” to tanks and other military vehicles. The slat armour comprises a metal frame which is mounted at a distance of approximately 500 mm from the vehicle. The frame comprises a plurality of horizontal struts or slats which are spaced apart at a distance selected to prevent penetration by shaped-charge warheads. The slat armour functions as a preliminary shield, causing the premature detonation of shaped-charge warheads or, if caught between slats, disabling damage of the shaped-charge. Slat armour has been used by both the British Army, on the Warrior APC and the American Army, on the Stryker APC. One disadvantage of the slat armour is that it is relatively heavy and adds a great deal of weight to the already very heavy vehicle.

An alternative to slat armour is disclosed in US 2007/0180983 A1, which discloses a protection system featuring a flexible packaged net with perimeter weighting housed in a deployment box releasably attached to a vehicle. One deployment subsystem includes an airbag packaged in the deployment box behind the net. A sensor subsystem detects an incoming threat and a fire control subsystem is responsive to the sensor subsystem and is configured to activate the deployment to inflate the airbag and deploy the net in the trajectory path of the incoming threat.

It is the object of the present invention to overcome some of the disadvantages of the prior art, or at least to offer an alternative system for counteracting the threat posed by RPGs.

According to the present invention there is provided a defence system comprising a net layer and a buffer layer, wherein the buffer layer is provided in front of the net layer.

The buffer layer is provided to give the defence system additional properties which cannot be attained using a net alone. The buffer layer and the net layer cover approximately the same surface area, such that only the buffer layer is visible when the defence system is viewed from the front. A projectile directed towards the defence system will impact with the buffer layer before impacting with the net layer.

The defence system according to the present invention is specifically intended to be used to defend against shaped-charge projectiles such as RPGs, in particular to diminish the effectiveness, or cause deformation, of the shaped-charges. As described above, the primary damage inflicted by a shaped-charge warhead, such as an RPG, is not caused by the explosion itself but by the shaped-charge jet which is generated. The primary function of the defence system according to the present invention is to deform the nose cone of the shaped-charge, thus preventing the piezoelectric initiator from generating a firing pulse, and therefore preventing the shaped-charge jet from forming. The defence system will typically be deployed at a distance of approximately 500 mm from the target object which it is protecting, such that even if the warhead does function, the shaped-charge jet will be partly diffused when it reaches the target object. It is envisaged that the present invention may be fitted to military vehicles, in much the same way as the conventional slat armour. However, the present invention offers significant advantages, particularly in terms of weight reduction. It is also envisaged that a defence system according to the present invention will be easier to repair.

The buffer layer functions as an environmental shield for the net layer and provides protection against the elements. In an embodiment of the invention the buffer layer may have one or more of the following properties: water-repellence; UV protection; IR shielding; camouflage patterning; non-stick surface; flame retardance.

In an embodiment of the invention the net layer is attached to the buffer layer. This ensures that the defence system can be provided as a single unit and also enables the net layer to be deployed in an open condition. The term “open condition” as used herein means that the net is extended such that it is free from sagging, but it does not need to be held under tension. It is important for the operation of the defence system that the net layer is free from sagging material when deployed, in order to reduce the likelihood of a direct hit on a net strand.

In an embodiment of the invention, the buffer layer defines a structure which supports the net layer in an open condition. The net layer may be in contact with the buffer layer, but it should be free to move. The buffer layer may conveniently be provided with means for securing it to a structure or vehicle to be protected. It is envisaged that a plurality of individual defence system sections may be combined together to form a complete shield for a structure or vehicle. A modular system such as this has the advantage of being easier to transport and it also facilitates easier repair of the system in the event of a hit, or other incident necessitating repair.

In an embodiment of the invention a backing layer may be provided such that the net layer is sandwiched between the buffer layer and the backing layer. The backing layer may be in contact with the net layer, but the net should still be free to move. In an embodiment of the invention the backing layer may be spaced apart from the net layer. The backing layer provides further structural support for the net layer and may form part of a housing in conjunction with the buffer layer.

In an embodiment of the invention the buffer layer comprises a layer of foam material. In an embodiment of the invention the foam material is a closed cell foam. In an embodiment of the invention the foam material has a density of less than 100 kg/m³. In an embodiment of the invention the foam material has a density of less than 90 kg/m³. In an embodiment of the invention the foam material has a density of less than 80 kg/m³. In an embodiment of the invention the foam material has a density of less than 70 kg/m³. In an embodiment of the invention the foam material has a density of less than 60 kg/m³. In an embodiment of the invention the foam material has a density of less than 50 kg/m³. In an embodiment of the invention the foam material has a density of less than 45 kg/m³. In an embodiment of the invention the foam material has a density of less than 40 kg/m³. In an embodiment of the invention the foam material has a density of less than 35 kg/m³. In an embodiment of the invention the foam material has a density of less than or equal to 30 kg/m³.

When the buffer layer is formed from a foam material, it may conveniently form a housing which supports the net layer. In an embodiment of the invention the backing layer may also be formed from a foam material with the same or different properties to the buffer layer.

In an embodiment of the invention a defence system comprises: a front foam buffer layer; a rear foam buffer layer; and a net layer, wherein the net layer is supported in open condition in an internal cavity defined by the front foam layer and the rear foam buffer layer. The defence system forms a self-contained unit which may be easily transported and deployed. The front and rear foam buffer layers define a housing which maintains the net in an “open” condition and prevents it from becoming tangled. As discussed above, the front and rear buffer layers also provide environmental protection for the net layer as it is not exposed to the elements.

In an embodiment of the invention the rear foam buffer layer comprises a back panel and a raised peripheral rim, and the front foam layer abuts the peripheral rim to define the internal cavity therebetween. In an embodiment of the invention the peripheral rim of the rear foam buffer layer further comprises an outer portion, which abuts the front foam layer, and an inner portion, which comprises a plurality of protrusions which are received within a mesh of the net to support the net in an open condition. The protrusions are advantageously received in the outermost meshes of the net, around its perimeter.

In an embodiment of the invention the net layer is spaced at least 60 mm from the back panel of the rear foam buffer layer. This spacing enables the net to act on a projectile before it hits the back panel of the defence system.

In an embodiment of the invention a spacer material is provided between the net layer and the rear foam buffer layer to maintain the spacing between the net layer and the rear foam buffer layer. In an embodiment of the invention the spacer material is a foam spacer layer. In an embodiment of the invention the spacer material is a reticulated foam layer.

The spacer material maintains a gap between the net layer and the rear foam buffer layer which, it is believed, is necessary to ensure optimum performance of the system. The spacer layer does not interfere with the operation of the system and, it is believed, plays no part in the interaction between the system and a projectile. The spacer material also provides additional structural support for the system.

In an embodiment of the invention the density of the front foam layer is lower than the density of the rear foam buffer layer. In an embodiment of the invention the front foam layer has a density of less than 45 kg/m³ and the rear foam buffer layer has a density of less than 80 kg/m³.

In an embodiment of the invention the front foam buffer layer and the rear foam buffer layer are the same density.

In an embodiment of the invention the defence system is provided with fixing means for attaching it to a vehicle or structure to be protected. In an embodiment of the invention the fixing means comprises a plurality of fixing members. In an embodiment of the invention the fixing members comprises spring mounted fixings.

In an embodiment of the invention the system further comprises an elasticated cord which engages with the net mesh around the perimeter of the net. In an embodiment of the invention the elasticated cord engages with the fixing means. In an embodiment of the invention the elasticated cord is attached to the net mesh at a plurality of locations around the perimeter of the net. The elasticated cord is provided to retain the shape of the net in the event of a hit from a projectile, e.g. an RPG, and it may be a continuous length of material. If the defence system is hit by a projectile then the net strands will typically break at the point of impact. If this happens the elasticated cord pulls the net back into shape after the hit and renders the defence system better capable of coping with multiple hits.

In addition to providing environmental protection, the foam material can also function to improve the performance of the defence system when counteracting the threat posed by an RPG. The objective of the defence system is to prevent the piezoelectric initiator from generating a firing pulse which triggers the formation of the shaped-charge jet. In the defence system the net layer is provided to disable an incoming RPG. Ignoring for the moment the role played by the buffer layer, the interaction of the net layer and an RPG will now be described.

In view of the fact that the net strands only occupy a small area of the total area covered by the net layer, i.e. most of the area is the open space, or net mesh, defined by the net strand, the likelihood is that the nose cone of an incoming RPG will be received in a net mesh. The nose cone is typically made from aluminum and nets will be selected such that the circumference of each net mesh is smaller than the maximum circumference of the nose cone of the commonly used RPGs in the particular location in which the defence system is deployed, such that the RPG cannot pass straight through the net. As it approaches the net the tip of the cone enters the net mesh. However, since the circumference of the net mesh is smaller than the circumference of the nose cone, the net strands begin to tighten against the nose cone as it passes through, causing the net to strangulate the nose cone. As mentioned above, the nose cone is hollow and the strangulation causes the nose cone to crumple, which in turn causes the firing mechanism to fail and prevents the shaped-charge jet from forming. Once the nose cone has been strangulated the remainder of the RPG acts on the net mesh and will typically cause the net strands to break. However, the damage caused by the body of the RPG will only be that of a high speed projectile, which is not comparable to the potential damage caused by a shaped-charge. In most cases it will be necessary to repair or replace the net layer after it has been hit. This is also the case in respect of the currently available slat armour.

As noted above, the net strands only occupy a small area of the total area covered by the net layer and the likelihood is that the nose cone of an incoming RPG will be received in a net mesh. However, the possibility exists that an incoming RPG will hit one of the net strands directly. If this happens then it is possible that the force of the impact will be sufficient to trigger the firing mechanism of the RPG and cause the shaped charge to form.

If an incoming RPG does make a direct hit on a net strand then the defence system will still provide some protection as the net layer will typically be positioned approximately 500 mm from the structure which is being protected. Consequently the effectiveness of the RPG will be reduced as the shaped charge will be formed 500 mm from the structure and will have lost some of its force by the time is impacts with the vehicle or structure being shielded.

Turning now to the role played by the foam material when the defence system is counteracting the threat posed by an RPG. As discussed above, the buffer layer is provided in front of the net layer. An incoming RPG will therefore make contact with the buffer layer before being received in a net mesh, or hitting a net strand. It is therefore important that the buffer layer does not trigger the firing mechanism of the RPG before the net layer had an opportunity to disable it.

When the buffer layer is formed from a foam material the foam preferably has a density of: less than 100 kg/m³; less than 90 kg/m³; less than 80 kg/m³; less than 70 kg/m³; less than 60 kg/m³; less than 50 kg/m³; less than 45 kg/m³; less than 40 kg/m³; less than 35 kg/m³; or less than or equal to 30 kg/m³, depending on the intended use of the defence system. Advantageously, the density of the foam should not be so high as to trigger the firing mechanism of a RPG upon impact. Consequently the RPG will pass through the foam buffer and interact with the net layer as described above. In situations where the RPG enters into a net mesh then it will be strangulated as described above and the interaction with the buffer layer will not affect the operation of the defence system.

However, the present inventors believe that a foam buffer layer can improve the effectiveness of the defence system in situations where an RPG makes a direct hit on a net strand. As described above, if an RPG impacts directly on a net strand there is a danger that the impact will be sufficient for the piezoelectric initiator to generate a firing pulse. The present inventors believe that a foam buffer layer can help to reduce the likelihood of the piezoelectric initiator generating a firing pulse in situations of direct impact on a net strand.

Without wishing to be bound by theory, it is believed that the foam buffer layer performs a number of functions. As discussed above, the density of the foam is such that it will not trigger piezoelectric initiator when the tip of the RPG strikes the foam buffer layer. Instead it is believed that a first part of the foam layer e.g. an outer layer, becomes embedded in the nose of the RPG. This provides the RPG with a soft tip which it is believed will prevent the RPG from cutting the net strands and thereby passing through the defence system. Secondly, it is believed that the inner layers of foam form an unstable column on the tip of the RPG which will tumble upon impact with a net strand so that the net strand is displaced sideways and the cone of the RPG is received in a net mesh. It is believed that the foam reduces the stress intensity transmitted into the nose upon impact and its low acoustic impedance properties reduce the likelihood that the piezoelectric initiator will generate sufficient electrical output to detonate the RPG.

In an embodiment of the invention the thickness of the foam buffer layer is in the range from 5 mm to 100 mm. In an embodiment of the invention the thickness of the foam buffer layer is in the range from 15 mm to 75 mm. In an embodiment of the invention the thickness of the foam buffer layer is in the range from 25 mm to 50 mm. In an embodiment of the invention the foam is a closed cell foam. It is believed that the cells of the foam form microscopic air-cushions which help to minimise the transference of force to the nose. In an embodiment of the invention the foam has a smooth outer surface.

In an embodiment of the invention the buffer layer may comprise a layer of lightweight fabric (fabric layer). In an embodiment of the invention the lightweight fabric is selected from the group consisting of one or more of: a rip-stop nylon fabric; an acrylic coated nylon; and a polyester. The fabric layer covers the net layer and provides environmental protection. One of the potential problems of a net-based system is that they can be difficult to keep clean in the field and dirt and debris can cause “hard points” to form on the net which can cause an RPG to detonate. The fabric layer shields the net layer from the environment and is easier to clean. The fabric layer advantageously has one or more properties selected from the group consisting of: water repellence; UV shielding; IR shielding; camouflage patterning; non-stick surface; flame retardant.

The strength of the lightweight fabric is selected such that it will allow an RPG to pass through without triggering the fuse. When an RPG hits the fabric layer it will pass through and engage the net layer as described above. In an embodiment of the invention the fabric layer has a mass of less than 160 g/m². In an embodiment of the invention the fabric layer has a mass of less than 155 g/m². In an embodiment of the invention the fabric layer has a mass of less than 150 g/m². In an embodiment of the invention the fabric layer has a mass of less than 145 g/m². In an embodiment of the invention the fabric layer has a mass of less than 140 g/m².

In an embodiment of the invention the net layer is supported at or near at least two adjacent corners, such that the body of the net hangs below. Advantageously the net layer is supported at at least three points, and more preferably four, to ensure that the net remains in an open condition when the vehicle is moving or in windy conditions. Testing has revealed the surprising result that the net does not require to be securely supported in order to be effective. In a typical example, a RPG will be travelling at velocities up to 300 ms⁻¹. Without wishing to be bound by theory, it is believed that in the time-frame in which the net acts on the nose cone, the cone will be strangulated before the load has had a chance to be transferred to the perimeter of the net. In tests conducted using slow motion cameras it has been possible to view the interaction between the net and the RPG. As mentioned above, the nose cone crumples when the net strands tighten around it. This renders the fuse inoperable and prevents formation of the shaped-charge jet. The remainder of the RPG then breaks through the net. It has been shown that at lower projectile velocities (in the region of 150 ms⁻¹) the RPG may be “caught” by the net and catapulted back. However, in order for this to happen the net must be securely supported by a strong frame.

In an embodiment of the invention the buffer layer comprises a bag-like structure which surrounds the net layer. The buffer layer provides environmental protection for the net layer. The bag-like structure may conveniently be provided with hook and loop fastenings along one edge, to provide easy access to the net layer, while at the same time ensuring that it is adequately shielded from the environment.

In an embodiment of the invention the net strands of the net layers comprise plastic fibres. It is preferred that the plastic fibres are synthetic plastic fibres and have one or more of the following properties: high tenacity; low elongation; high strength to weight ratio; low density; and soft finish. As will be discussed in more detail below, it is desirable for the net strands to be thin. Consequently, suitable fibres must be high tenacity in order to perform the desired function. Similarly, the fibres must be made of a relatively low elongation material. If the fibres were made of a high elongation material then they would stretch on impact and may allow the nose cone to pass through and impact with the target. In order to improve handling it is desirable for the textile armour to be as light as possible.

Testing has determined that it is desirable for the fibres to be high strength but with a “soft and fluffy” finish. Although the term “soft and fluffy” does not describe technical features of the fibres it describes a desirable characteristic of them. In the event that a nose cone of a RPG hits one of the net strands directly it is preferred that the fibre is deflected and the nose cone continues into a net mesh, rather than firing and forming a shaped-charge jet. If the net strand has a “hard” finish then the possibility exists that the RPG will fire. It is therefore preferred that the fibres do not have a “hard” or resilient surface finish.

Although it is desirable for the fibres to have a “soft” finish, they must also be high tenacity as they need to be capable of strangulating the nose cone of a shaped-charge warhead before they fail. In an embodiment of the invention the net strands comprise ultra high molecular weight polyethylene fibres, such as Dyneema® or Spectra®. Alternatively, the net strands may be made from other high-strength man-made fibres, e.g. para-aramid synthetic fibres, such as Kevlar®, hybrid materials, such as Zylon® or Vectran®, or any other suitable material.

Traditional nets tend to have knotted intersections where net strands are knotted in order to form the net mesh. It has been discovered that these knots form so-called “hard” surfaces which may cause a RPG to fire if it impacts directly onto the knot. Consequently, if a knotted construction is used then it is preferred that the knot is as small as possible to reduce the likelihood of a direct hit occurring.

In an embodiment of the invention the net layer comprises a knotless mesh construction. Alternatively, the net may comprise a woven construction. In both of these constructions the intersections between nets strands are much less likely to cause a shaped-charge to fire if a direct hit occurs. It is believed that the particular construction of the net does not play any particular role in disabling the shaped-charge. The only consideration for the net construction is that the intersections are as small and “soft” as possible.

As discussed above, the primary function of the net strands is to strangulate the nose cone of a shaped-charge warhead and prevent it from firing. In order to perform this function it is preferred that the net strands are as thin as possible in order to increase the likelihood of the nose cone entering one of the net meshes, rather than hitting one of the net strands. It is a requirement of the invention that the net is not tensioned and that it is presented in an open condition. The net should not be allowed to sag. If the net material is permitted to sag then it will tend to bunch up, thus increasing the likelihood of a warhead hitting the net strands. Consequently, the net material should be held in an open condition, although it need not necessarily be taut.

As mentioned above, it is conceivable that if the tip of the nose cone hit directly onto one of the net strands then this may cause the RPG to fire. However, even if this was to happen the defence system would still provide some protection as it will normally be located at least 500 mm from the target object which it is shielding. Consequently the shaped-charged jet will be formed at least 500 mm from the target and its effectiveness will be decreased.

In an embodiment of the invention the net strands of the net layer have a diameter of less than 10 mm. In an embodiment of the invention the net strands have a diameter of less than 6 mm. The only limiting factor to the diameter of the net strands is the availability of materials from which to manufacture them. Ideally the net strands will have as small a diameter as possible. Using currently available materials it is preferred that the diameter of the net strands is in the range from 3-6 mm. As technology advances it is envisaged that it will be possible to utilise net strands having a diameter of less than 3 mm. The dimensions of the net strands are measured in accordance with BSI Aerospace Series Standard BS6F 100:1998.

As discussed above, the object of the textile armour is to disable a shaped-charge warhead, such as a RPG. This is achieved by strangulating the nose cone of the RPG, thus preventing it from firing. A number of different RPGs are currently available and it envisaged that over time more will be developed. The size of the warhead tends to vary between different RPGs. For example, a RPG-7 propels a warhead with a diameter of 90 mm and a RPG-18 propels a warhead with a diameter of 64 mm. Although a general form of the textile armour will be capable of disabling more than one size of warhead, such as the RPG-7 and the RPG-18, it is preferred that the textile armour is selected to counteract the specific threat, i.e. an RPG-7 specific textile armour.

In an embodiment of the invention the circumference of each individual mesh section of the net is less than the maximum circumference of the RPG warhead which the net is designed to counteract. It is envisaged that one net could be utilised against more than one type of RPG, but in most conflict situations there will usually be one type of RPG which is most common. The selection of a suitable mesh size ensures that the RPG cannot pass straight through the net mesh. Each individual mesh section is defined as the shape defined by the intersection of the net strands. The mesh may be a variety of shapes, such as square, rectangular, triangular, circular, pentagonal, hexagonal octagonal or any combination of these shapes. The circumference of the net mesh is the total distance around the perimeter of the net mesh. For example, in a square net mesh with sides of 45 mm the circumference will be 180 mm.

In an embodiment of the invention the circumference of each individual mesh section is less than, or equal to, two-thirds of the maximum circumference of the RPG warhead. This has been found to be the optimum mesh size which allows for as open a net as possible, while ensuring that the net is capable of strangulating the nose cone of an RPG warhead. It is believed that if the circumference of the mesh section is greater than two-thirds of the maximum circumference of the RPG warhead, then the possibility exists that the warhead will pass through the net and impact with the target object. It is also desirable to have as open a net as possible in order to minimise the likelihood of the warhead impacting with the net strands. Consequently, it has been discovered that the optimum circumference of each mesh section is two-thirds of the maximum circumference of the nose cone of the RPG which the net is designed to disable.

As discussed above the RPG-7 propels a warhead with a maximum diameter of 90 mm. The maximum circumference of such a warhead will be approximately 283 mm. Consequently, the optimum circumference of each mesh section in a defence system designed to counteract the RPG-7 would be approximately 188 mm. In the case of a square net mesh this would require sides of approximately 47 mm. In the case of a square or rectangular net mesh the sides will typically be in the range from 20-100 mm.

In order to improve the functionality of the textile armour system it is preferred that the buffer layer is provided with a camouflage colouring. More preferably, the buffer layer is provided with a suitable camouflage garnish to compliment the colouring of the surroundings in which the system will be used. The use of such camouflage is well known.

According to a second aspect of the present invention, there is provided a modular defence system comprising a plurality of defence systems as described above. In an embodiment of the invention the individual defence system elements are provided with fixing means for attaching them to a vehicle or structure. In an embodiment of the invention the individual defence system elements are provided with means for connecting them with each other. In an embodiment of the invention each defence system element comprises a plurality of fixing means. In an embodiment of the invention the fixing means comprise spring mounted fixing elements.

According to a third aspect of the present invention there is provided a net comprising a plurality of intersecting net strands, wherein at least some of the net strands are braided net strands with a foam core running through them. In an embodiment of the invention the density of the foam is less than 100 kg/m³, more preferably less than 90 kg/m³ and most preferably less than 80 kg/m³.

As discussed above, if a shaped-charge projectile, such as an RPG, makes a direct hit on a net strand then there is a possibility that the fuse will be triggered and a shaped-charge jet will be formed. Without wishing to be bound by theory, the present inventors believe that the introduction of a foam core into a braided net strand will reduce the overall density of the net strand such that the tip of a shaped-charge will displace the net strand without the fuse being triggered. The tip of the shaped-charge projectile will then pass into the net mesh defined by the net strand and the net will act on the shaped-charge as described above.

According to a forth aspect of the present invention there is provided a net comprising a plurality of intersecting net strands, wherein at least some of the nets strands are encapsulated in foam. In an embodiment of the invention the density of the foam is less than 100 kg/m³, more preferably less than 90 kg/m³ and most preferably less than 80 kg/m³.

It is believed that a net strand which is encapsulated in foam will minimise the transference of force to the nose of the RPG and reduce the likelihood of the piezoelectric initiator triggering the firing pulse.

According to an aspect of the invention there is provided a defence system comprising a net layer and a buffer layer, as hereinbefore described, wherein the net layer comprises a plurality of intersecting net strands with at least some of the net strands being braided net strands having a foam core running through them.

According to an aspect of the invention there is provided a defence system comprising a net layer and a buffer layer, as hereinbefore described, wherein the net layer comprises a plurality of intersecting net strands with at least some of the net strands being encapsulated in a foam material.

For a better understanding of the present invention reference will now be made to the accompanying drawings showing solely by way of example, an embodiment of the invention and, in which:

FIG. 1 shows a perspective view of an embodiment of a defence system attached to a vehicle;

FIG. 2 shows a perspective view of the defence system of FIG. 1 removed from the vehicle;

FIG. 3 shows a partially cut away view of the defence system of FIG. 2;

FIG. 4 shows a side sectional view defence system of FIGS. 2 and 3;

FIG. 4A shows a side sectional view of an alternative embodiment of the defence system of FIGS. 2 and 3;

FIG. 5A shows a perspective view of a second embodiment of a defence system;

FIG. 5B shows a close up view of a portion of the defence system of FIG. 5A;

FIG. 6A shows a perspective view of a third embodiment of a defence system;

FIG. 6B shows a close up view of a portion of the defence system of FIG. 6A;

FIG. 7 shows a perspective view of an embodiment of a defence system;

FIG. 8 shows a partially cut away view of the defence system of FIG. 7;

FIG. 9 shows a perspective view of an embodiment of a defence system;

FIG. 10 shows a partially cut away view of the defence system of FIG. 9;

FIG. 10A shows a close up of a portion of the defence system of FIG. 10;

FIG. 11 shows a side sectional view of the defence system of FIGS. 9-10A.

FIG. 12 shows an exploded view of an embodiment of a defence system; and

FIG. 13 shows a side sectional view of an assembled defence system of FIG. 12.

Referring firstly to FIG. 1, this shows an embodiment of a defence system 2 mounted on a military vehicle 50. The construction of various embodiments of the defence system 2 will be discussed in more detail with reference to FIGS. 2-13. The present invention relates to a defence system 2 which may be utilised to protect a vulnerable target 50, such as a vehicle, building or other object, from damage caused by a shaped-charge warhead, such as a rocket propelled grenade (RPG).

Shaped-charge warheads, such as RPGs are capable of penetrating steel and armour and, therefore, pose a particular problem for tanks and armoured personnel carriers (APC) in combat situations. In order to limit the damage caused by an impact from a RPG a variety of preliminary shields have been developed which either aim to defuse the RPG, to prevent the shaped-charge from forming, or they aim to detonate the RPG at a safe distance from the target object, to lessen the damage cause by the shaped-charge.

The defence system shown in FIGS. 1-4A comprises a net layer 4, a foam buffer layer 6 and a foam backing layer 7 and it is mounted onto a vehicle 50 by means of a plurality of flexible stanchions 8. The flexible stanchions 8 comprise a base 10, a spring mid-section 12, which is secured to the base 10, and a support strut 14, which is attached to the spring 12 and the net layer 4 and foam layers 6, 7.

The flexible stanchions 8 are secured to the vehicle 50 by means of a plurality of screws (not shown) which pass through the base 10 of the flexible stanchions 8 and engage with a panel of the vehicle 50. Due to the fact that the defence system 2 is relatively light-weight (at least compared to currently available systems), the attachment points on the vehicle 50 do not need to be structural. This increases the flexibility of the defence system 2 as almost any point on the vehicle 50 can be used. Although screws are used to secure the defence system 2 to the vehicle 50 other suitable fixing means may also be used, as will be readily apparent to the skilled person. The vehicle 50 may be provided with specific points to engage with the flexible stanchions 8, e.g. appropriately sized holes to receive the fixing screws, or the flexible stanchions 8 may simply be secured to a vehicle 50 by drilling holes at the desired locations.

The flexible stanchions 8 support the net layer 4 and foam layers 6, 7 in a spaced relationship to the vehicle 50. The net layer 4 and foam layers 6, 7 are positioned approximately 500 mm from the vehicle 50 in order to effectively counteract the threat posed by RPGs, as will be discussed in more detail below.

Only one defence system 2 is shown in FIG. 1, but it is envisaged that a plurality of individual defence system elements 2 could be combined in a modular defence system. The number of defence system elements 2 required will depend on the size of the structure or vehicle which is being protected, but it is envisaged that many defence system elements 2 could be combined to protect large structures. Conversely, it may only require one or two defence system elements 2 to protect the side of a small vehicle. The flexible stanchions 8 are provided slightly in-board from the perimeter of each defence system element 2 in order to allow the edges of each defence system element 2 to abut an adjacent defence system element 2 and avoid any gaps.

Referring now to FIGS. 2-4A, which illustrate one defence system element 2 in more detail. As discussed in relation to FIG. 1, the defence system 2 comprises a net layer 4, a foam buffer layer 6, a rear backing layer 7 and four flexible stanchions 8, which secure the defence system 2 to a structure or vehicle 50 in use of the defence system 2. The flexible stanchions 8 comprise a base 10, a spring mid-section 12 which is secured to the base 10 and a support strut 14 which is attached to the spring 12 and the net layer 4 and foam layers 6, 7. As can best be seen in FIGS. 4 and 4A, the support strut 14 of each flexible stanchion 8 passes through the backing layer 7 and the front foam layer 6 and secures the net layer 4 and foam layers 6, 7 at a predetermined distance from the vehicle 50. The support strut 14 comprises a shoulder 14 a, which abuts a rear surface of the backing layer 7, and a support pin 15, which passes through the backing layer 7 and the front foam layer 6. A nut 17 secures the front foam layer 6 on the support pin 15. The support pins 15 pass through a corner mesh of the net layer 4 and provide support for the net layer 4.

As can be best seen in FIGS. 3-4A, the net layer 4 is encapsulated between the front foam layer 6 and the backing layer 7, which is also made of foam. The foam is a closed cell foam with a density of 80 kg/m³. The foam layers 6, 7 provide structural support and environmental protection for the net layer 4. The front foam layer 6 and backing layer 7 are approximately 35 mm thick.

The front surface of the front foam layer 6, i.e. the one which faces away from the vehicle 50, is smooth and can be easily cleaned to avoid the build up of debris on it surface. The front foam layer 6 and the foam backing layer 7 are water repellant, non-stick and they are provided with a camouflage patterning to suit the terrain in which the defence system 2 is intended to be used. The foam layers 6, 7 provide environmental protection for the net layer 4 and also provide UV protection, infra-red (IR) shielding (to disguise the IR signature of the vehicle or structure) and they are flame retardant.

The front foam layer 6 and the backing foam layer 7 are both provided with a small lip 6 a, 7 a around their perimeter, such that when they come together a cavity 16 is defined between the foam layers 6, 7. The perimeter edge of the net layer 4 is “trapped” between the meeting lips 6 a, 7 a of the front foam layer 6 and the backing layer 7 at the top of the cavity 16 to hold it securely in place, but it is free to move within the cavity 16. In this embodiment the net 4 hangs down from the top edge 16 a of the cavity 16, but in an alternative embodiment the net 4 may be held around its perimeter by the lips 6 a, 7 a of the foam layers 6, 7. In any event, the net 4 should be supported in open condition, but it should not be tensioned. The flexible stanchions 8 provide additional support for the net 4 by engaging with a mesh of the net 4 at each corner of the net 4. The foam layers 6, 7 are bonded together using a suitable adhesive, but any suitable means for connecting two foam layers 6, 7 could be utilised.

FIG. 4A shows an alternative version of the system 2 illustrated in FIG. 4, in which a cavity 9 is provided behind the net 4. The system 2 is substantially identical to the system of FIG. 4 and the same numbering has been used. In the system of FIG. 4A the lip 7 a around the perimeter of the backing foam layer 7 is slightly larger than in FIG. 4. This ensures that when the net 4 is trapped between the meeting edges of the lips 6 a, 7 a a cavity 9 is defined behind the net 4. The lip 7 a extends 60 mm from the main body of the backing form layer 7 such that the net 4 is held away from the main body of the backing foam layer 7 by approximately this distance. It is believed that this distance is sufficient to allow the net 4 to act on a projectile before it impacts with the main body of the backing foam layer 7.

The net layer 4 comprises a plurality of net strands 18 made from Dyneema® SK75 (manufactured by DSM Dyneema B.V.) which are formed with knotless intersections, as is well known in the art. The net strands 18 have a diameter of approximately 5 mm and a strength of approximately 14 kN, and they define a plurality of regular net meshes 19. The circumference of the net meshes 19 is approximately equal to two thirds of the circumference of the nose cone of the RPG which the defence system 2 is designed to counteract. For example, the RPG-7 propels a warhead with a maximum diameter of 90 mm. The maximum circumference of such a warhead will be approximately 283 mm. Consequently, the circumference of each mesh section 19 in a defence system 2 designed to counteract the RPG-7 would be approximately 188 mm. In the case of a square net mesh this would require sides of approximately 47 mm.

The illustrated embodiment of the invention comprises a net layer 4 with net strands 18 having a diameter of approximately 5 mm. The properties of the net layer 4 can be varied by using net strands 18 of differing diameters. For example, Dyneema® SK75 with a diameter of 5.5 mm has a strength of approximately 17.2 kN and Dyneema® SK75 with a diameter of 6 mm has a strength of approximately 23.1 kN. Similarly, it is envisaged that net strands 18 having a smaller diameter could also be used in a defence system 2 according to the present invention. An optimum embodiment of the net layer 4 would have net strands 18 with the smallest possible diameter and it is envisaged that new materials will be developed in the future which will make net strands 18 with a diameter of less than 3 mm easily achievable.

The operation of the defence system 2 will now be discussed in more detail. The primary function of the defence system 2 is to disable the nose cone of a RPG to prevent the piezoelectric initiator in the nose from generating a firing pulse which will trigger the formation of a shaped-charge. This is achieved by strangulating the nose cone of the RPG. Two basic situations are envisaged when a RPG hits a defence system 2 as illustrated in FIGS. 1-4A. The most common scenario is that the RPG hits the front foam layer 6 and passes through and the nose is received in one of the net meshes 19. The density of the front foam layer 6 is selected such that it will not trigger the firing mechanism of the RPG. In this case the foam plays no function in disabling the RPG. Since the circumference of the net mesh 19 is smaller than the circumference of the nose cone, the net strands 18 begin to tighten against the nose cone as it passes through, causing the net layer 4 to strangulate the nose cone. As mentioned above, the nose cone is hollow and the strangulation causes the nose cone to crumple, which in turn causes the firing mechanism to fail and prevents the shaped-charge jet from forming. Once the nose cone has been strangulated the remainder of the RPG acts on the net mesh 19 and will typically cause one or more of the net strands 18 to break. However, the damage caused by the body of the RPG will only be that of a high speed projectile, which is not comparable to the potential damage which would be caused by a shaped-charge. In most cases it will be necessary to repair or replace the net layer 4 and foam layers 6, 7 after the defence system 2 has been hit.

The second scenario envisaged is that the RPG hits the front foam layer 6 and again passes through, but this time the path of the RPG is directly towards a net strand 18 of the net layer 4. In prior art systems if a RPG hits a net strand 18 then it is possible that the force of the impact would be sufficient to trigger the firing mechanism of the RPG and cause a shaped charge to form. In a defence system 2 according to the present invention the addition of the front foam layer 6 serves to reduce the likelihood of sufficient force being transferred to the piezoelectric initiator in the nose of the RPG to trigger detonation.

As noted above, the density of the foam is such that when the RPG hits the front foam layer 6 it will pass straight through. In addition, the density of the foam is such that it will not trigger the piezoelectric initiator when the tip of the RPG strikes the front foam layer 6. Instead, without wishing to be bound by theory, it is believed that a first part of the foam layer 6 e.g. an outer layer, becomes embedded in the nose of the RPG. This provides the RPG with a soft tip which it is believed will prevent the RPG from cutting the net strands 18 and thereby passing through the defence system 2. Secondly, it is believed that the inner layers of foam form an unstable column on the tip of the RPG which will tumble upon impact with a net strand 18 so that the net strand 18 is displaced sideways and the cone of the RPG is received in a net mesh 19. It is believed that the foam reduces the stress intensity transmitted into the nose upon impact and its low acoustic impedance properties reduces the likelihood that the piezoelectric initiator will generate sufficient electrical output to detonate the RPG.

Turning now to FIGS. 5A and 5B which show an alternative embodiment of a defence system 20. The defence system 20 comprises a net 22 which is formed from a plurality of intersecting net strands 24, 26 and a plurality of knotless intersections 25, as is known in the art. The nets strands 24, 26 are braided net strands and they have a foam core 28 running through them. The net strands 24, 26 are formed from Dyneema® SK75 and the foam core 28 is a closed cell foam with a density of 80 kg/m³.

The defence system 20 is provided with a buffer layer 27 in the form of a layer of rip-stop nylon fabric. The buffer layer 27 illustrated in FIG. 5A is partially cutaway to show the net layer 22 below, but in use it will cover the net layer 22 completely to provide environmental protection for the net layer 22. The rip-stop nylon has a mass of 140 g/m². The rip-stop nylon can be easily wiped clean and it also provides the defence system 20 with the following useful properties: water repellence; UV shielding; IR shielding; camouflage patterning; non-stick surface; flame retardant properties.

The defence system 20 can be mounted onto a vehicle or structure by means of four flexible stanchions 30 which are positioned at the corners of the net 22. The flexible stanchions 30 are of the same construction as the flexible stanchions 8 of FIGS. 1-4A and comprise a base 32, a spring mid-section 34 which is secured to the base 32 and a strut support 36 which is attached to the spring 34 and the net 22. The flexible stanchions 30 hold the net 22 in an open condition, i.e. the net 22 does not sag, but the net 22 is not held under tension. The strut supports 36 pass through a corner mesh of the net layer 22 and provide support for the net layer 22 to ensure the net layer 22 is held in an open condition even when the vehicle is moving or when conditions are windy.

The flexible stanchions 30 can be secured to a vehicle or structure by means of a plurality of screws which pass through the base of the flexible stanchions 30 and engage with the vehicle or structure. Although screws are used to secure the defence system other suitable fixing means may also be used, as will be readily apparent to the skilled person. The vehicle or structure may be provided with specific points to engage with the fixings members, e.g. appropriately sized holes to receive the fixing screws, or the fixing members may simply be secured to a vehicle or structure by drilling holes at the desired locations. Due to the fact that the defence system 20 is relatively light-weight (at least compared to currently available systems), the attachment points on the vehicle or structure do not need to be structural. This increases the flexibility of the defence system 20 as almost any point on the vehicle or structure can be used.

The flexible stanchions 30 support the net 22 in a spaced relationship to the vehicle or structure. In use, the net 22 will be positioned approximately 500 mm from the vehicle or structure in order to effectively counteract the threat posed by RPGs, as will be discussed in more detail below.

It is envisaged that a plurality of individual defence system elements 20 could be combined in a modular defence system. The number of defence system elements 20 required will depend on the size of the structure or vehicle which is being protected, but it is envisaged that many defence system elements 20 could be combined to protect large structures. Conversely, it may only require one or two defence system elements 20 to protect the side of a small vehicle.

The basic operation of the net 22 in strangulating a RPG is the same as that discussed above in relation to the net portion of the defence system illustrated in FIGS. 1-4A. However, as noted above, there is a potential problem if a RPG impacts directly onto a net strand 24, 26. Without wishing to be bound by theory, it is believed that the foam core 28 in the net 22 of FIGS. 5A and 5B minimises the transference of force to the nose of the RPG and enables the net strand 24, 26 to be pushed to one side without the piezoelectric initiator trigger detonation of the RPG.

Turning now to FIGS. 6A and 6B which show an alternative embodiment of a defence system 40. The defence system 40 comprises a net 42 which is formed from a plurality of intersecting net strands 44, 46 and a plurality of knotless intersections 45, as is known in the art. The nets strands 44, 46 are braided net strands formed from Dyneema® SK75. Each net strand 44, 46 is encapsulated in a layer of foam 48. The foam is a closed cell foam with a density of 80 kg/m³.

The defence system 40 is provided with a buffer layer 47 in the form of a layer of rip-stop nylon fabric. The buffer layer 47 illustrated in FIG. 6A is partially cutaway to show the net layer 42 below, but in use it will cover the net layer 22 completely to provide environmental protection for the net layer 22. The rip-stop nylon has a mass of 140 g/m². The rip-stop nylon can be easily wiped clean and it also provides the defence system 40 with the following useful properties: water repellence; UV shielding; IR shielding; camouflage patterning; non-stick surface; flame retardant properties.

The defence system 40 can be mounted onto a vehicle or structure by means four flexible stanchions 50 which are positioned at the corners of the net 42. The flexible stanchions 50 are of the same construction as the flexible stanchions 8 of FIGS. 1-4A and comprise a base 52, a spring mid-section 54 which is secured to the base 52 and a strut support 56 which is attached to the spring 54 and the net 42. The flexible stanchions 50 hold the net 42 in an open condition, i.e. the net 42 does not sag, but the net 42 is not held under tension. The strut supports 56 pass through a corner mesh of the net layer 42 and provide support for the net layer 42 to ensure the net layer 42 is held in an open condition even when the vehicle is moving or when conditions are windy.

The flexible stanchions 50 can be secured to a vehicle or structure by means of a plurality of screws which pass through the base of the flexible stanchions 50 and engage with the vehicle or structure. Although screws are used to secure the defence system other suitable fixing means may also be used, as will be readily apparent to the skilled person. The vehicle or structure may be provided with specific points to engage with the fixings members, e.g. appropriately sized holes to receive the fixing screws, or the fixing members may simply be secured to a vehicle or structure by drilling holes at the desired locations. Due to the fact that the defence system 40 is relatively light-weight (at least compared to currently available systems), the attachment points on the vehicle or structure do not need to be structural. This increases the flexibility of the defence system 40 as almost any point on the vehicle or structure can be used.

The flexible stanchions 50 support the net 42 in a spaced relationship to the vehicle or structure. In use, the net 42 will be positioned approximately 500 mm from the vehicle or structure in order to effectively counteract the threat posed by RPGs, as will be discussed in more detail below.

It is envisaged that a plurality of individual defence system elements 40 could be combined in a modular defence system. The number of defence system elements 40 required will depend on the size of the structure or vehicle which is being protected, but it is envisaged that many defence system elements 40 could be combined to protect large structures. Conversely, it may only require one or two defence system elements 40 to protect the side of a small vehicle.

The basic operation of the net 42 in strangulating a RPG is the same as that discussed above in relation to the net portion of the defence system illustrated in FIGS. 1-4A and 5A and 5B. However, as noted above, there is a potential problem if a RPG impacts directly onto a net strand 44, 46. Without wishing to be bound by theory, it is believed that the foam cover 48 of FIGS. 6A and 6B minimises the transference of force to the nose of the RPG and enables the net strands 44, 46 to be pushed to one side without the piezoelectric initiator triggering detonation of the RPG.

FIGS. 7 and 8 show a further embodiment of a defence system 60 according to the present invention. The defence system 60 is broadly similar to the defence system 2 shown in FIGS. 1-4A, but in place of a front foam layer 6 and a backing layer 7 the net layer 62 in the defence system 60 is provided with a buffer layer 64 in the form of a layer of lightweight rip-stop nylon. The buffer layer 64 encapsulates the net layer 62 and provides environmental protection for the net layer. The rip-stop nylon has a mass of 140 kg/m² which ensures that an RPG will pass through the buffer layer without sufficient force being transmitted to the nose to cause the piezoelectric initiator to trigger detonation of the RPG. The rip-stop nylon buffer layer 64 can be easily wiped clean and it also provides the defence system 60 with the following useful properties: water repellence; UV shielding; IR shielding; camouflage patterning; non-stick surface; flame retardant properties.

The defence system 60 comprises a plurality of flexible stanchions 66 which are used to mount the system 60 on to a vehicle or structure. The flexible stanchions 66 are the same as the flexible stanchions 8 described in relation to the embodiment of the invention described in FIGS. 1-4A. The flexible stanchions support the net 62 in an open, non-tensioned condition. It is also envisaged that there may be a weak line of stitching along the top edge of the buffer layer which attached the net to the buffer layer to support it in an open, non-tensioned condition. A line of weak stitching may also be employed in the defence systems 20, 40 shown in FIGS. 5A and 6A.

In an alternative embodiment of the invention a defence system 60 as described with reference to FIGS. 7 and 8 may be provided with a spacer layer of reticulated foam between the net layer 62 and the rear of the buffer layer 64. The spacer layer serves to maintain a gap between the net layer 62 and the rear of the buffer layer 64 and also serves to provide structural support to the system 60. The reticulated foam adds rigidity to the system 60, but does not interfere with the operation of the system 60. The use of a spacer layer of reticulated foam is described in more detail with reference to FIGS. 12 and 13 and this description is generally applicable in the present case.

The operation of the defence system 60 is broadly the same as other net based defence systems. It is believed that the buffer layer 64 only provides environmental protection for the net layer and that it does not play a part in counteracting the RPG.

FIGS. 9-11 show a further embodiment of a defence system 70. The defence system 70 is broadly similar to the defence system 2 shown in FIGS. 1-4A. The defence system 70 comprises a net layer 72, front and rear foam buffer layers 74, 76 and four flexible stanchions 78, which can be used to secure the defence system 70 to a structure or vehicle. The flexible stanchions 78 are the same as those illustrated in FIGS. 1-4A and comprise a base 80, a spring mid-section 82, which is secured to the base 80, and a support strut 84. The means of attachment between the stanchions 78 and the front and rear foam buffer layers 74, 76 is slightly different to that illustrated in respect of the systems shown in FIGS. 1-8. The different means of attachment are shown by way of example only and the skilled person will appreciate that both means of attachment can be used on any of the systems described in this application. The means of attachment in the system 70 are in the form of 3-part bushes 94 which will be discussed in more detail below.

As can best be seen in FIG. 11, the 3-part bushes 94 comprise a central cylindrical portion 95 which is provided with an annular projection 96 towards one end. The central cylindrical portion 95 passes through the rear foam buffer layer 76 and the annular projection 96 rests on a lip 86, which extends around the perimeter of the rear foam buffer layer 76, as described in more detail below. A front plug 97 then passes through the front foam buffer layer 74 and engages in an interference fit within the central cylindrical portion 95 to secure the front foam buffer layer 74 to the rear foam buffer layer 76. A rear plug 98 passes through the back of the rear foam buffer layer 76 and engages in an interference fit with the central cylindrical portion 95. The support strut 84 of the stanchion 78 then engages with the rear plug 98 to enable the system 70 to be deployed.

The front and rear foam layers 74, 76 form a housing which encapsulates the net 72. The defence system 70 is light-weight and easy to handle. The defence system 70 may be part of a modular system which could be used to protect a vehicle, structure or other vulnerable target. It can be replaced in the field more easily that some currently available systems. The net 72 is housed inside the foam layers 74, 76 and has a degree of freedom to move. The foam layers 74, 76 provide environmental protection for the net layer 72, as well as performing a function in the event of a direct hit on a net strand, as described in relation to the defence system 2 shown in FIGS. 1-4A.

As can best be seen in FIGS. 10 and 10A, an elasticated nylon cord 92 is wound through the net mesh at the periphery of the net 72 and around the 3-part bushes 94. The elasticated cord 92 is a continuous length of material, and it is provided to retain the shape of the net 72 in the event of a hit from a projectile, e.g. an RPG. If the defence system 70 is hit by a projectile then the net strands will typically break at the point of impact. If this happens the elasticated cord 92 pulls the net 72 back into shape after the hit and renders the defence system 70 better capable of coping with multiple hits. Although the elasticated cord 92 is only shown in respect of the embodiment of the invention shown in FIGS. 9-11 it is clear that it could also be incorporated into the other embodiments of the invention disclosed in FIGS. 1-8 and 12-13. A plurality of clips (not shown) connect the elasticated cord 92 to the net 72 and are provided around the periphery of the net 72. These clips serve to retain the integrity of a major portion of the elasticated cord 92 in the event that it is subject to a direct hit. In this case the elasticated cord 92 may break in a region between two clips, but it will remain taut along the remainder of its length. Typically at least four clips are provided, located inboard from the corner, but it will be clear to the skilled person that more or less clips could also be used.

The front layer of foam 74 is constructed from a flexible foam with a density of 30 kg/m³. The surface of the front layer 74 is smooth, so that it can be easily wiped clean to prevent the build up of debris. The rear foam layer 76 is constructed from a closed cell rigid foam with a density of 30 kg/m³. The front foam layer 74 and the rear foam layer 76 are water repellant, non-stick and they are provided with a camouflage patterning to suit the terrain in which the defence system 70 is intended to be used. The foam layers 74, 76 provide environmental protection for the net layer 72 and also provide UV protection, infra-red (IR) shielding (to disguise the IR signature of the vehicle or structure) and they are flame retardant. In an alternative embodiment, the defence system 2, 70 can be provided with a camouflage cover (not shown) which is a replaceable bag-like structure which surrounds the system 2, 70 and can be changed to suit the surroundings. The camouflage cover may be made from a rip-stop nylon material similar to that used in respect of the systems 20, 40, 60 shown in FIGS. 5A-8. The openings of the camouflage cover may conveniently be secured by hook and loop fastenings, e.g. Velcro®, or by any other suitable means.

The rear foam layer 76 is provided with a back panel 85 and a raised lip 86 around its perimeter, which extends outwardly with respect to the back panel 85. A plurality of cylindrical protrusions 88 are provided on the lip 86 extending in a direction away from the back panel 85. The protrusions 88 are sized such that they may engage with a mesh of the net 72 when the defence system 70 is assembled. The protrusions 88 serve to hold the net 72 loosely in place, along with the 3-part bushes which each engage with a portion of the net mesh in the corner of the net 72. The lip 86 has an outer edge 86 a which extends to the same height as the protrusions 88 and upon which the front foam layer 74 sits when the system 70 is assembled. The rear foam layer 76 is formed from a single piece of foam, with the back panel 85, lip 86, outer edge 86 a and protrusions 88 being machined out of the foam. The foam layers 74, 76 are bonded together using a suitable adhesive, but any suitable means for connecting two foam layers 74, 76 could be utilised.

The lip 86 has a height of 60 mm, measured in a direction away from the back panel 85, such that when the net 72 rests on the lip 86 a void 99 is created behind the net 72. The void 99 can best be seen in FIG. 11. This gives the net a degree of freedom of movement and permits the net 72 to hang freely within the system 70 and act on a projectile in a natural manner. It is envisaged that a larger void 99 could be provided in the defence system 70, but for operational flexibility it is preferred that the void 99 is not too large.

The net layer 72 comprises a plurality of net strands made from Dyneema® SK75 (manufactured by DSM Dyneema B.V.) which are formed with knotless intersections, as is well known in the art. The net strands have a diameter of approximately 5 mm and a strength of approximately 14 kN, and they define a plurality of regular net meshes. The circumference of the net meshes is approximately equal to two thirds of the circumference of the nose cone of the RPG which the defence system 70 is designed to counteract. For example, the RPG-7 propels a warhead with a maximum diameter of 90 mm. The maximum circumference of such a warhead will be approximately 283 mm. Consequently, the circumference of each mesh section in a defence system 70 designed to counteract the RPG-7 would be approximately 188 mm. In the case of a square net mesh this would require sides of approximately 47 mm.

The system 70 functions in the same general manner as the system 2 of FIGS. 1-4A and the operation will not be described again.

FIGS. 12 and 13 show a further embodiment of a defence system 100. The defence system 100 of FIGS. 12 and 13 is substantially the same as the system 70 shown in FIGS. 9-11 and the same numbering will be used for like parts.

FIG. 12 is shown as an exploded view to aid understanding of the construction of the system 100 and to highlight the differences between the system 100 and the system 70 of FIGS. 9-11. The defence system 100 includes a layer of reticulated foam 110 between the net layer 72 and the rear foam buffer layer 76. The reticulated foam layer 110 is a rigid foam and has a plurality of holes 120 machined out of it to help reduce the total weight of the system 100. The reticulated foam has a density of 35 kg/m³ prior to profiling and approximately 13 kg/m³ after the holes 120 have been machined.

As can best be seen in FIG. 13, the reticulated foam layer 110 acts as a spacer to maintain the gap of 60 mm between the net layer 72 and the rear foam buffer layer 76. The reticulated foam layer 110 sits in the void 99 between the net layer 72 and the rear foam buffer layer 76 and is in contact with both. The reticulated foam 110 also provides structural support to the system 100, which is particularly important to maintain the integrity of the system 100 in the extreme temperatures to which it is envisaged that the system 100 will be exposed.

Without wishing to be bound by theory, it is believed that the reticulated foam layer 110 does not play any part in the detonation of a shaped-charge projectile. The operation of the system 100 is believed to be identical to that of the system 70 illustrated in FIGS. 9-11. The layer of reticulated foam could also be incorporated into the system 2 shown in FIG. 4A.

Although the present invention has been described with reference to the embodiments shown in FIGS. 1-13, it will be clear to the person skilled in the art that alternative embodiments of the invention could be devised within the scope of the claims. 

1. A defence system comprising a net layer and a buffer layer, wherein the buffer layer is provided in front of the net layer.
 2. A defence system according to claim 1, wherein the buffer layer has one or more properties selected from the group consisting of: UV protection; water resistance; IR shielding; camouflage pattering; non-stick surface; flame retardance.
 3. A defence system according to claim 1, wherein the net layer is attached to the buffer layer.
 4. A defence system according to claim 3, wherein the buffer layer supports the net in an open condition.
 5. A defence system according to claim 1, further comprising a rear buffer layer, wherein the net is sandwiched between the rear buffer layer and the buffer layer in front of the net.
 6. A defence system according to claim 1, wherein the buffer layer comprises a layer of a foam material.
 7. A defence system according to claim 6, wherein the foam material has a density of less than 100 kg/m³.
 8. A defence system according to claim 6, wherein the foam material is a closed cell foam.
 9. A defence system comprising: a front foam buffer layer; a rear foam buffer layer; and a net layer, wherein the net layer is supported in an open condition in an internal cavity defined by the front foam buffer layer and the rear foam buffer layer.
 10. A defence system according to claim 9, wherein the rear foam buffer layer comprises a back panel and a raised peripheral rim, and wherein the front foam buffer layer abuts the peripheral rim to define the internal cavity therebetween.
 11. A defence system according to claim 10, wherein the peripheral rim of the rear foam buffer layer further comprises an outer portion, which abuts the front foam buffer layer, and an inner portion, which comprises a plurality of protrusions which are received within a mesh of the net to support the net in an open condition.
 12. A defence system according to claim 10, wherein the net layer is spaced at least 60 mm from the back panel of the rear foam buffer layer.
 13. A defence system according to claim 9, wherein a spacer material is provided between the net layer and the rear foam buffer layer to maintain the spacing between the net layer and the rear foam buffer layer.
 14. A defence system according to claim 13, wherein the spacer material is a reticulated foam layer.
 15. A defence system according to claim 9, wherein the defence system is provided with fixing means for attaching it to a vehicle or structure to be protected.
 16. A defence system according to claim 9, wherein the system further comprises an elasticated cord which engages with the net mesh around the perimeter of the net and with fixed points on the defence system to retain the net in an open condition.
 17. A defence system according to claim 16, wherein the elasticated cord is attached to the net mesh at a plurality of locations around the perimeter of the net.
 18. A defence system according to claim 1, wherein the buffer layer comprises a layer of lightweight fabric.
 19. A defence system according to claim 18, wherein the lightweight fabric is a rip-stop nylon fabric.
 20. A defence system according to claim 18, wherein the lightweight fabric has a mass of less than 160 g/m².
 21. A defence system according to claim 18, wherein the buffer layer comprises a bag-like structure which surrounds the net layer.
 22. A defence system for mitigating effects of a projectile and comprising a net layer and a buffer layer, wherein the buffer layer is provided in front of the net layer so that the buffer layer encounters a projectile before the net layer does.
 23. A defence system according to claim 22, wherein the buffer layer comprises a layer of a foam material. 